LeetCode 101. Symmetric Tree (javascript)

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Example 1:

Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:

Input: root = [1,2,2,null,3,null,3]
Output: false

Constraints:

• The number of nodes in the tree is in the range [1, 1000].
• -100 <= Node.val <= 100

Solution:

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {boolean}
 */
var isSymmetric = function(root) {
    return isSameTree(root, root); 
};

function isSameTree(t1, t2) {
    if (t1 === null && t2 === null) return true;
    if (t1 === null || t2 === null) return false;
    return t1.val === t2.val && isSameTree(t1.left, t2.right) && isSameTree(t1.right, t2.left); 
}